Particle-mediated delivery of biological material, particularly genetic material, into living cells and tissue has emerged as an important tool of plant and animal biotechnology. Transient and long-term expression of introduced genetic material from target cells, as well as successful integration of introduced DNA into germ cells, have been demonstrated in a wide variety of microorganisms, plants, and animals.
One limitation of existing particle-mediated delivery devices is the form in which the biological sample must be provided. In such prior devices, the biological sample is coated onto the surface of small, dense carrier particles comprised of a dense material such as gold or platinum. The coated particles are themselves arranged on a carrier surface, such as a rigid surface or metal plate, or a planar carrier sheet made of a fragile material such as mylar. The carrier surface is then accelerated toward a target, and the coated carrier particles are dislodged from the surface thereof for delivery to a target. This approach has several advantages as well as some disadvantages. One advantage provided by the use of a carrier surface, such as a planar sheet, is that a very uniform spread of accelerated particles can be delivered into a target surface. One disadvantage is that each carrier surface must be prepared individually and used only once, making use of such devices time-consuming and inefficient. This is particularly problematic when repetitive delivery must be carried out. Each coated carrier surface is also relatively large and must be handled with care to avoid damage or contamination during loading of a particle acceleration device. It may also be difficult to distinguish the coated side of a carrier surface from the uncoated side, which increases the possibility of improper positioning of the carrier surface in an acceleration device. Such improper positioning can reduce throughput and result in substantial waste of biological samples.
The distribution or spread of carrier particles delivered from a particle acceleration apparatus can be critical in some applications, particularly when the biological material being delivered is comprised of genetic material. For example, in applications where germline transformation events are desired, the need to control the delivery pattern of carrier particles is substantially more acute than in other applications, such as where only transient expression of introduced genetic material is needed. When an infrequent germline transformation event is desired, it is necessary to uniformly accelerate the carrier particles toward a large target area to increase the likelihood that one or more target cells will be transformed. Thus, one approach to such transformations has been to distribute the coated carrier particles as a monolayer on a relatively large carrier surface. This helps maximize the number of cells receiving particles under precisely uniform conditions. In applications where coated particles are accelerated into cells to induce transient gene expression in somatic tissues such as skin, there is a less compelling need to provide a uniform particle distribution, since adequate expression can be accomplished even when a relatively low number of cells receive the particles.
In particle acceleration applications wherein coated particles are used to deliver nucleic acid vaccines preparations, genetic material encoding an antigenic determinant is delivered into a target tissue. In those cells that have been successfully transfected with the genetic material, transient expression of a protein or peptide encoded by the genetic material ensues, eliciting an immune response against the protein or peptide. These and other therapeutic or medicinal applications of particle acceleration technologies present practical considerations such as the need to maintain the cleanliness and, possibly, the sterility of an apparatus used to deliver the particles to a recipient. These issues take on particular significance when the apparatus is to be used in large-scale immunization projects. For these and other reasons, then, the art has a particular need for a particle acceleration apparatus that can be used without contaminating samples or targets, as well as an apparatus that avoids inappropriate delivery of residual particles trapped in the particle delivery path.